Wrong code at -O2 on x86_64-linux_gnu since Clang-15

[shao-hua-li]

clang at -O2 produced the wrong code.

Bisected to b22ffc7, which was committed by @aeubanks

Compiler explorer: https://godbolt.org/z/MxrnaqTqc

% cat a.c
int printf(const char *, ...);
int a;
static int b;
short(c)(short d, int e) { return d >> e; }
char *f(int d, char *e) {
  if ((d & 1) == 0)
    return e;
  switch (d) {
  case 7:
  case 49:
  case 1:
    return "";
  case 11:
    return "0";
  case 3:
    return "0";
  }
  return "1";
}
char g(int d) {
  char h = 0, i = *f(d, &h);
  return i;
}
char j(int d) {
  for (;;) {
    if (g(d + 7) + d)
      return 0;
    for (; b - 30; b+=0)
      ;
  }
}
void k() {
  int l = -8, m = c(l, 8);
  j(m);
}
int main() {
  k();
  printf("%X\n", a);
}
% 
% clang -O0 a.c && ./a.out
0
% clang -O2 a.c && ./a.out
%

[nikic]

Reduced test case:

; RUN: opt -S -passes=dse < %s
define void @test() {
entry:
  %a = alloca i8
  store i8 0, ptr %a
  %call = call ptr @f(ptr %a) memory(none) nounwind willreturn
  %v = load i8, ptr %call
  %cmp = icmp ne i8 %v, 1
  call void @llvm.assume(i1 %cmp)
  ret void
}

declare ptr @f(ptr)
declare void @llvm.assume(i1)

This ends up dropping the store.

[nikic]

Similar case as https://reviews.llvm.org/D153464.